Yarn texturing

ABSTRACT

A yarn texturing process wherein the yarn is false twisted and heat set and wherein the yarn is passed through an elongated heat transfer means and is supported therein on a cushion of fluid flowing in the heat transfer means.

This invention relates to the texturing of yarns by false twist crimping. According to the present invention there is provided a texturing process in which a yarn advances through one or more heat transfer zones to a false twisting means wherein heat is transferred to and/or from the yarn by a transverse fluid flow which also supports the yarn in a curved path.

The preferred fluid is air though other gaseous mixtures or single gases may be employed including steam.

In particular the yarn may be cooled by a transverse fluid flow.

The curved path may comprise an arc so that the yarn direction after the curved path is different from the yarn direction before the curved path. Alternatively the curved path may conveniently take the form of a 360° loop so that the yarn leaves the curved path travelling in the same direction as that in which it entered the curved path. Depending upon the relative positions of heating and/or false twisting means other shapes of curved path may also be used such as, for example, an arc in one direction of curvature followed by an arc in another direction of curvature, or a succession of such alternating arcs providing other 2 or 3-dimensional sinuous yarn paths.

If the logarithm of the difference between the yarn temperature and the ambient air temperature at a point in the cooling zone is plotted against the distance along the yarn path from the end of the heating zone, then a roughly straight line is usually obtained with a slope of - k/v where v is the yarn velocity and k is the cooling rate. It is found that in a process according to the invention the cooling rate is greater and more consistent between different yarns, and that the yarns are more stable and yield a more uniform textured yarn product than in processes in which no air guide is used to assist in yarn cooling before the false twisting means.

The following examples illustrate but do not limit the present invention.

Exampls 1-16

A 250 decitex 45 filament polyester yarn derived from polyethylene terephthalate was passed at 440 meters per minute over a 1.8 meter flat plate with a surface temperature of 250°C to a false twister, and the following tables (I and II) gives some results from 16 experiments under different cooling conditions. Experiments 1-4 and 13-16 are examples of the invention, while 5-12 are comparative examples. In each of the examples of the invention a circular air guide was used providing a yarn path loop of 360° at a diameter of about 9.5 cm in a continuous slot 0.0038 cm wide. An air flow of 220 liters per minute was provided at the slot and this was sufficient the cushion the yarn in its circular path so that it did not come into contact with any solid guiding surfaces.

In example 5 an unheated aluminium cooling plte 0.97 meters long was used to stabilise and support the yarn. In examples 6, 7 and 8 no such stabilising plate was used and the yarn vibrated between the heater and the false twister. Under these vibrating conditions the cooling rate in ambient air was higher but less consistent. In examples 1-5 the cooling rate in the air guide was both very high and very consistent, and the yarn was quite stable so the cooling rate in the ambient air before and after the guide, unassisted by a cooling plate, was quite low. It is common to use a second heater to stabilise the yarn after crimping. Table II shows that the resultant yarn shrinkage is much less dependent on primary and secondary heater temperatures when there is efficient cooling by an air guide before the false twister.

                                      TABLE I                                      __________________________________________________________________________      EFFECT OF REDUCING COOLING DISTANCE                                           __________________________________________________________________________     Example No.     1   2   3   4   5   6   7   8                                  __________________________________________________________________________     Cooling Distances:                                                             Heater to twister, meters                                                                      1.23                                                                               0.97                                                                               0.77                                                                               0.50                                                                               1.23                                                                               1.23                                                                               0.90                                                                               0.76                               Heater to air guide, m                                                                         0.97                                                                               0.70                                                                               0.40                                                                               0.22                                                                               --  --  --  --                                 Air guide circumference, m                                                                     0.31                                                                               0.31                                                                               0.31                                                                               0.31                                                                               --  --  --  --                                 Air guide to twister, m                                                                        0.21                                                                               0.21                                                                               0.21                                                                               0.21                                                                               --  --  --  --                                 Total cooling length, m                                                                        1.49                                                                               1.22                                                                               0.92                                                                               0.74                                                                               1.23                                                                               1.23                                                                               0.90                                                                               0.76                               __________________________________________________________________________     Yarn Temperatures:                                                             Leaving heater °C                                                                       248 249 247 247 233 240 230 236                                Entering air guide °C                                                                   173 181 214 226 --  --  --  --                                 Leaving air guide °C                                                                    49  51  60  62  --  --  --  --                                 Entering twister °C                                                                     46  47  57  58  102 68  86  121                                __________________________________________________________________________     k in air guide °C/°C/min                                                         1020                                                                               1010                                                                               960 970 --  --  --  --                                 k in ambient air °C/°C/min                                                       79  96  75  86  180 250 246 191                                __________________________________________________________________________

                                      TABLE II                                     __________________________________________________________________________     EFFECT OF REDUCING TEMPERATURES                                                __________________________________________________________________________     Example No.    9   10  11  12  13  14  15  16                                  __________________________________________________________________________     Temperatures:                                                                  Crimp setting heater                                                           (primary) °C                                                                           240 235 230 225 225 230 235 240                                 Post crimp stabilising                                                         heater (secondary) °C                                                                  195 190 185 180 180 185 190 195                                 __________________________________________________________________________     Cooling Rates:                                                                 k in air guide °C/°C/min                                                        --  --  --  --  1070                                                                               1030                                                                               1020                                                                               1040                                k in ambient air °C/°C/min                                                      209 180 168 168 63  76  72  82                                  __________________________________________________________________________     Yarn shrinkages %                                                                             15.5                                                                               16.7                                                                               21.4                                                                               22.9                                                                               14.0                                                                               14.0                                                                               12.5                                                                               12.6                                __________________________________________________________________________

                                      TABLE II                                     __________________________________________________________________________     EFFECT OF REDUCING TEMPERATURES                                                __________________________________________________________________________     Example No.    9   10  11  12  13  14  15  16                                  __________________________________________________________________________     Temperatures:                                                                  Crimp setting heater                                                           (primary) °C                                                                           240 235 230 225 225 230 235 240                                 Post crimp stabilising                                                         heater (secondary) °C                                                                  195 190 185 180 180 185 190 195                                 __________________________________________________________________________     Cooling Rates:                                                                 k in air guide °C/°C/min                                                        --  --  --  --  1070                                                                               1030                                                                               1020                                                                               1040                                k in ambient air °C/°C/min                                                      209 180 168 168 63  76  72  82                                  __________________________________________________________________________     Yarn shrinkages %                                                                             15.5                                                                               16.7                                                                               21.4                                                                               22.9                                                                               14.0                                                                               14.0                                                                               12.5                                                                               12.6                                __________________________________________________________________________

Example 17

Using the same false twist crimping process described in the previous examples, the circular air guide was replaced by a linear air guide comprising a continuous slot 0.018 cm wide, 3.5 om deep and 20 cm long. Ceramic guides had to be used before and after this linear device in order to keep the yarn in the slot while deflected by the air into an arcuate path. This device was broadly similar in its cooling effect to that of the circular air guide, as illustrated by Table III.

                  TABLE III                                                        ______________________________________                                                            0.10 m diameter                                                                            0.20 m long                                     Cooling Means      circular    linear                                                             air guide   air guide                                       ______________________________________                                         Air flow liters/min                                                                               220         114                                             Draw speed m/min   580         580                                             ______________________________________                                         Cooling Distances:                                                             Heater to air guide, m                                                                            0.20        0.30                                            Length in air guide, m                                                                            0.31        0.20                                            Air guide to false twister, m                                                                     0.48        0.68                                            ______________________________________                                         Temperatures:                                                                  Leaving heater °C                                                                          188         191                                             Entering air guide °C                                                                      170         168                                             Leaving air guide °C                                                                        61          80                                             Entering twister °C                                                                         50          64                                             k in air guide °C/°/min                                                             1040        1110                                            ______________________________________                                    

Examples 18-20 (Table IV)

In examples 18 and 19 the air guide used was similar to that described in example 17, but in example 20 the guide was V-shaped in cross-section. This guide had a continuous slot 0.008 inches wide at its base which diverged at an angle of 10° for 3.5 cm. All three examples were of draw texturing processes.

                                      TABLE IV                                     __________________________________________________________________________     Example     18        19        20                                             __________________________________________________________________________     Process     Simultaneous draw                                                                        Simultaneous draw                                                                        Sequential draw                                            texturing texturing texturing                                      Yarn        Polyethylene                                                                             Polyethylene                                                                             Polyhexamethylene                                          terephthalate                                                                            terephthalate                                                                            adipamide                                                  350 decitex                                                                              350 decitex                                                                              210 decitex                                                30 filament                                                                              30 filament                                                                              20 filament                                    Drawing speed m/min                                                                        600       900       570                                            Draw ratio  2.1       2.1       2.7                                            Guide length, cm                                                                            50        50        27                                            Slot width, inches                                                                         0.008     0.008     --                                             Air pressure, psi                                                                           10        10       8.3                                                                            cu ft/min (air                                                                 flow)                                          Yarn temperature                                                               entering guide, °C                                                                  174       170       172                                            Yarn temperature                                                               leaving guide, °C                                                                    60        90       120                                            Cooling rate k                                                                 °C/°C/min                                                                    705       630       396                                            __________________________________________________________________________

It has also been found that similar types of air guides may be very advantageously used for heating the yarn before the false twister.

It is known that as yarn speed is increased longer heating paths are required to maintain the same twist setting time. Also, it is known that for efficient twist setting it is necessary for all or virtually all of the twist to run back right through the heating zone so twist snubbing must be avoided in the heating zone. Thus it has been proposed to reverse the direction of yarn travel across a heater so that it can pass back and forth and by using cushions of air to support the yarn at the reversal points instead of solid surfaces or idler rolls, there is virtually no twist snubbing action.

However in the present invention the need for long heaters and for yarn reversals between passes over heaters is avoided.

Thus, the present invention provides a process for false twist crimping an advancing yarn by twisting, heating, cooling and detwisting in which the yarn is heated by fluid flowing transversely thereto and supporting it in a curved path. The heat transfer between fluid and yarn under these circumstances is high and twist snubbing action is negligible.

The guides of this invention may be used on their own to heat the yarn or alternatively may be used in conjunction with conventional heaters, e.g. flat plate heaters. Where appropriate, hot air issuing from the guides may be recirculated.

The experiments listed in Table V relate to draw texturing a 520 decitex 30 filament polyester yarn derived from polyethylene terephthalate of birefringence 6.2 × 10⁻ ³ at a take off speed of 440 meters per minute. The draw ratio in each case was 3.16 and the apparatus comprised feed roll, heater, friction bush false twister and draw roll. In the Table experiments A to F are examples of the invention while experiments G to H are control experiments using conventional flat plate heaters.

                                      TABLE V                                      __________________________________________________________________________     Ex.                                                                               Heater Type                                                                              Air Flow                                                                           Indicated                                                                           Yarn Temp                                                                            Yarn Temp                                                                            Path length                                                                          Heating REMARKS                                     cu  Heater                                                                              Entry to                                                                             Leaving                                                                              in Heater                                                                            rate                                                ft/min                                                                             Temp.                                                                               Heater                                                                               Heater                                                                               cm    k*                                                      °C                                                                           °C                                                                            °C   °C/°C/min                __________________________________________________________________________     A  Circular air guide                                                                       8   173  80    143   31.4  945     Used with feed roll at            0.0038 cm slot width                         116°C. Draw roll                                                        speed                             9.5 cm diameter                              580 m/min.                     B  Circular air guide                                                                       8   220  193   210   31.4  825     Used after 1.8 m                  0.0038 cm slot width                         primary heater at                                                              220°C.                     9.5 cm diameter                              D/R speed 580 m/min            C  Linear air guide                                                                         9   140  72    116   20.3  940     Used with feed roll at            0.018 cm slot width                          118°C. D/R speed           20 cm length                                 580 m/min                      D  Linear air guide                                                                         9   205  62    134   20.3  865     Used with feed roll at            0.018 cm slot width                          118°C. D/R speed           20 cm length                                 580 m/min                      E  V-shaped air guide                                                                       8   205  62    136   20.3  910     Used with feed roll at            0.0038 cm slot width                         118°C. D/R speed           20 cm length                                 580 m/min                      F  V-shaped air guide                                                                       8   205  23    155   20.3  940     No other heating means            0.0038 cm slot width                         used. D/R speed                   20 cm length                                 340 m/min                      G  1.8 meter --  200  23    190   1.8m  400     Control. D/R speed                Flat plate heater                            580 m/min                      H  1.8 meter --  200  23    185   1.8m  346     Conrol. D/R speed                 Flat plate heater                            580 m/min                      __________________________________________________________________________      *Calculated as above but where the logarithm of the difference between th      heater temperature and the yarn exit temperature is plotted against the        length of the heater.                                                    

Preferably the yarn is both heated and cooled while being supported in curved paths by fluids flowing transversely to the yarn. 

We claim:
 1. A yarn texturing process in which yarn advances from twist setting means to false twisting means wherein the improvement comprises passing the yarn through a continuous elongated slot in heat transfer means positioned between the twist setting and false twisting means where the yarn is cooled by a transverse fluid flow which also supports the yarn in a curved path within the slot.
 2. A process according to claim 1 wherein the yarn is both heated and cooled by a transverse fluid flow.
 3. A process according to claim 1 wherein the curved path comprises one or more arcs so that the yarn direction after the curved path is different from the yarn direction before the curved path.
 4. A process according to claim 3 wherein the yarn direction remains unchanged.
 5. A process according to claim 1 wherein the yarn is derived from a polyester.
 6. A process according to one claim 1 wherein the yarn is derived from a polyamide.
 7. A process according to claim 5 wherein the yarn is drawn prior to being textured.
 8. A process according to claim 7 wherein the yarn is sequentially drawn and textured.
 9. A process according to claim 5 wherein the yarn is simultaneously drawn and textured. 